The present invention relates to electrostatically actuated devices and more particularly to silicon-based actuators having a corrugated, multi-layer silicon membrane structure for increased rigidity.
Cross-reference is made to co-pending application U.S. patent application Ser. No. 09/416,329, (D/98191) entitled xe2x80x9cMicro-Electro-Mechanical Fluid Ejector And Method Of Operating Samexe2x80x9d, filed on Oct. 12, 1999, U.S. patent application Ser. No. 09/687,096, (D/A0783) entitled xe2x80x9cMethod And Apparatus For Preventing Degradation Of Electrostatically Actuated Devicesxe2x80x9d, filed on Oct. 13, 2000, and U.S. patent application Ser. No. 09/768,688, (D/A0784Q) entitled xe2x80x9cMethod For Fabricating A Micro-Electro-Mechanical Fluid Ejectorxe2x80x9d filed concurrently herewith, the entire disclosure of which is hereby incorporated by reference.
In ink-jet printing, droplets of ink are selectively ejected from a plurality of drop ejectors in a printhead. The ejectors are operated in accordance with digital instructions to create a desired image on a print medium moving past the printhead. The printhead may move back and forth relative to the sheet in a typewriter fashion, or in the linear array may be of a size extending across the entire width of a sheet, to place the image on a sheet in a single pass.
The ejectors typically comprise actuators connected to both a nozzle or drop ejection aperture and to one or more common ink supply manifolds. Ink is retained within each channel until there is a response by the actuator to an appropriate signal. In one embodiment of the ejector, the ink drop is ejected by the pressure transient due to volume displacement of an electrostatically- or magnetostatically-actuated deformable membrane, which typically is a capacitor structure with a flexible electrode, fixed counter electrode, and actuated by a voltage bias between the two electrodes.
Silicon-based actuators can also be employed in micro-electromechanical devices that can be used for pumping and switching, and wherein for example, silicon based actuators are, respectively, used for microfluid pumping, and optical switching. Fluids are pumped due to the volume displacement of an electrostatically- or magnetostatically-deformable membrane, which is a capacitor structure with a flexible electrode, fixed counter electrode, and actuated by a voltage bias between the two silicon electrodes. Optical switching occurs by the displacement of optical elements as a result of actuation due to electrostatic or magnetostatic interactions with other on-chip elements or a magnetostatic device package. For example, in optical switching a mirror can be employed as the optical element using electrostatic actuators to provide the displacement.
This capacitor structure which incorporates a deformable membrane for these silicon-based actuators can be fabricated in a standard polysilicon surface micro-machining process. It can be batch fabricated at low cost using existing silicon foundry capabilities. The surface micro-machining process has proven to be compatible with integrated microelectronics, allowing for the monolithic integration of the actuation with associated addressing electronics.
A problem associated with using such devices as actuators in ink jet printing is that to generate the pressure required for ejecting ink drops from the printhead, the membrane must be sufficiently rigid. Apart from increasing the membrane thickness or using stiffer material, which may not be allowed in a standardized surface-micromachining fabrication process, one solution is to make the membrane smaller. However, as the membrane shrinks, so does the displacement volume, and thus the size of the drop emitted. Therefore, it is desirable to increase the ink jet drop ejector ability to eject useful-sized drops of ink without decreasing the size of the ejector or increasing the thickness of the membranes.
There is provided an electrostatic device including a substrate having an insulating layer thereon; a conductor formed on said insulating layer; a membrane adjacent to said conductor, said membrane having a corrugated, multi-layer structure; and an actuator chamber formed by removing a sacrificial layer between said membrane and said conductor, said membrane flexing toward said conductor when a voltage bias is applied thereto.
These and other aspects of the invention will become apparent from the following description, the description being used to illustrate a preferred embodiment of the invention when read in conjunction with the accompanying drawings.